In many modern communication architectures, a communications platform, such as a call server, an application server, a softswitch, and/or an interne protocol (IP) multimedia subsystem (IMS) solution provides communications services to communications endpoints over a packet network. In some instances, the communications platform provides basic connectivity between endpoints as well as more advanced features, such as caller identification, call forwarding, three-way calling, and call waiting, among others. Thus, connectivity with the communications platform is important in providing not only advanced features but also basic connectivity between endpoints.
A fault can occur in a communication network that disconnects the communications platform from various parts of the network, depending on the location of the fault. A fault can occur due a failure of a router or a physical link, as examples. A router or a physical link connected to the router may fail for any of a number of reasons. For example, a link may be severed, or any of a number of physical components on the router may fail due to normal wear and tear or due to an exceptional event, such as a power surge. Regardless of the reason for the fault, an endpoint may lose basic connectivity with other endpoints if connection with a communications platform is lost for any reason.
Emergency standalone (ESA) service refers to the ability to provide some limited calling services, such as 911 service, even if there is a failure in the network that causes a loss of connectivity to the communications platform and therefore a loss of connectivity to other endpoints and their users. Conventional approaches to providing ESA service focus on providing basic connectivity at the level of an access node that serves a group of endpoints. When an access node is disconnected from the communications platform, the access node itself can provide some basic connectivity to endpoints directly connected to the access node. Furthermore, conventional approaches also address grouping of access nodes, provided each of the access nodes connects endpoints using an access technology common to each of the access nodes. Grouping of access nodes can provide regional access between endpoints connected to the various access nodes. However, modern telecommunications networks can comprise access nodes that span a number of different access transport technologies and protocols, particularly with respect to upstream interfaces with a communications platform and/or downstream interfaces with one or more endpoints. For example, some networks include access nodes that provide various combinations of analog telephony, legacy digital telephony, and packet-based telephony, such as voice over Internet protocol (VoIP), through a broad range of protocols, including network-based call signaling (NCS), media gateway control protocol (MGCP), gateway control protocol (H.248), H.323 and session initiation protocol (SIP). In some embodiments, the transport technologies and communications interfaces and protocols may be collectively referred to as access technologies. The provision of regional survivable communications involving access nodes with disparate access technologies has not been addressed previously.